Each year, approximately 400,000 to 600,000 Americans suffer from cardiac arrythmia such as tachyarhythmia which often worsens into ventricular fibrillation in which the heart twitches furiously but pumps no blood, usually causing sudden death. Defibrillation is referred to as the non-synchronized delivery of electrical energy to the heart to correct ventricular fibrillation.
Research in the field of cardioverters/defibrillators has been in progress for many years.
U.S. Pat. No. 4,499,907 describes a transvenous cardioversion lead which is adapted for use with presently available external defibrillation units. The lead is provided with circuitry which reduces energy from the defibrillator to a safe level for use with transvenous defibrillation. The lead has four electrodes, of which two are implanted within the right ventricle of the heart and the other two implanted within the superior vena cava.
U.S. Pat. No. 4,641,656 describes a four-electrode lead system designed to maximize the efficiency of electrical energy and depolarizing the heart and terminating tachycardia or defibrillation. The electrodes are described to be mounted around the heart wherein the regime for applying pulses and optimizing electrode size and placement are altered to provide a more efficient system.
U.S. Pat. No. 4,690,155 describes a monophasic action potential contact electrode catheter for use in the study of the electrophysiology of cardiac tissue. The catheter includes an elongated tubular body having a hub assembly at its proximal end portion and a distal tip portion.
U.S. Pat. No. 4,662,377 describes an automatic implantable cardioverter/defibrillator having an electrode system which includes an intravascular catheter with a first electrode adjacent the distal end of the catheter, and a second electrode at the proximal end. The catheter electrode is inserted intravenously to a position such that the distal electrode is positioned in the right ventricular apex of the heart and the proximal electrode is positioned in the superior vena cava region of the heart.
A flexible patch electrode is also electrically connected to the proximal electrode and subcutaneously positioned inside the thoracic cavity. The patch electrode is described as being flexible, conformal, generally planar having a metallic mesh on the surface facing the heart.
Many of the references cited require implantation of electrodes within the thoracic cavity and myocardium thus subjecting a patient to the surgical opening of the thoracic cavity and possible risks of infection. Also, many of the cardioverter/defibrillator systems require large discharges of electrical energy to the heart (10 joules or more). Furthermore, many will not maintain close contact with the endocardium, requiring higher electrical energy and, or causing burning of the cardiac tissue.
There is a need for a flexible, compliant defibrillation patch and system capable of maintaining close contact of the electrode material to muscle tissue, thereby requiring lower energy discharges (four+joules) without burning muscle tissue.